Having a 24' iMAC is a lot of fun. Mine happily dual boots between 'Tiger' and 'Vista' but sometimes there are things I'd like to do using both...
And then came VMware Fusion! Not only does it virtualise my BottCamp install but it also has this super feature called Unity. Unity mixes up my Tiger and Vista experiences allowing me to run Windows applications directly from the Dock. I can minimize Windows applications to the Dock, switch between Windows or Mac applications with Exposé, find and instantly launch any Windows application, drag and drop files between Windows and the Mac, and use familiar Mac keyboard shortcuts to copy and paste between Windows and Mac applications.
This gives me the best of both and gives fusion a huge lead over Parallels.
The second fun thing I've been doing on my MAC is using Microsoft's Remote Desktop Connector for the MAC. This allows me to mange a Microsoft machine straight off the MAC desktop. I recently had the interesting experience of RDC to my development boxes Virtual Image running under MS's Virtual PC. This meant I could dev onto this remote machine!!